Snail retracted in its shell; the normally black scales and shell are rusty from being stored in alcohol.Image courtesy Anders Warén.

Scientists have discovered snails living at the bottom of the ocean whose protruding feet are covered with hard, mineralized scales arranged like tiles on a roof.

Nothing like them has ever been found before. The snails resemble fossilized animals that lived hundreds of millions of years ago. Yet, according to DNA analysis, the newly discovered species of snail evolved relatively recently.

The snail lives near black-smoker chimneys, or hydrothermal vents, at the bottom of the Indian Ocean, and the researchers suspect that the scales are formed from dissolved minerals that flow out of the chimneys.

“It's a very striking and peculiar animal,” says Anders Warén of the Swedish Museum of Natural History in Stockholm, Sweden, who led the study. He has studied snails living in hot springs for more than 20 years.

The scales are made of pyrite, a mineral better known as “fool's gold” for its shiny luster. A group of researchers isolated about 20 of the snails using a remotely operated submersible during an expedition to the Indian Ocean in April 2001.

The snail's scales may protect it from predatory snails that also live near the vents. The predatory snails inject venomous darts into their prey, but the darts are too short to penetrate the newly discovered snail's armor.

The snail, or gastropod, has adapted to survive the harsh conditions near the vents. The water is full of hydrogen sulfide, which is twice as poisonous as cyanide gas.

In a tidy symbiotic match, the snail offers its interior as a home for bacteria, which in turn make the proteins and carbohydrates that the snail uses for food. The snail and its shell are about four centimeters long.